ATL: ISAAC - Post-Tropical - Discussion

[wxman76]

Tropical Storm ISAAC Forecast Discussion

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000
WTNT44 KNHC 240859
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 AM EDT FRI AUG 24 2012

DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT ISAAC REMAINS
POORLY ORGANIZED. WHILE THE 850-MB FLIGHT LEVEL CENTER WAS WELL
SOUTH OF THE PREVIOUSLY ESTIMATED SURFACE CENTER LOCATION...
DROPSONDE DATA SUGGEST THAT THE SURFACE CENTER REMAINS FARTHER
NORTH. FLIGHT LEVEL AND SFMR WINDS SUPPORT MAINTAINING THE
INTENSITY AT 40 KT FOR THIS ADVISORY...WHILE THE AIRCRAFT FOUND A
MINIMUM PRESSURE OF 1000 MB. GIVEN THE CURRENT LACK OF ORGANIZATION
OF THE INNER CORE...ONLY LIMITED STRENGTHENING IS FORECAST BEFORE
THE CYCLONE BEGINS TO INTERACT WITH HISPANIOLA IN THE NEXT 24
HOURS. AFTER THAT TIME LITTLE CHANGE IS FORECAST AS ISAAC INTERACTS
WITH PORTIONS OF CUBA. LATER IN THE PERIOD...ISAAC SHOULD HAVE AN
OPPORTUNITY TO STRENGTHEN OVER THE STRAITS OF FLORIDA AND THE GULF
OF MEXICO...AND THE NHC FORECAST IS CLOSE TO THE LGEM MODEL AT DAYS
4 AND 5. IT SHOULD BE NOTED THAT THERE IS SIGNIFICANT UNCERTAINTY
IN TROPICAL CYCLONE INTENSITY PREDICTIONS AT 3 TO 5 DAYS.

THE LONG TERM INITIAL MOTION ESTIMATE IS A HIGHLY UNCERTAIN
275/13...AS THE INITIAL POSITION ESTIMATE IS BASED ON A BLEND OF
RECENT FIXES AND CONTINUITY. THE TRACK MODEL GUIDANCE CONTINUES TO
BE IN GENERALLY GOOD AGREEMENT ON THE RESUMPTION OF A WEST-
NORTHWESTWARD AND THEN NORTHWESTWARD MOTION IN THE NEXT 24 HOURS AS
THE SUBTROPICAL RIDGE NORTH OF ISAAC WEAKENS. THIS GENERAL MOTION
SHOULD CONTINUE THROUGH DAY 4...WHEN A TURN MORE TOWARD THE NORTH
IS SHOWN AS A SHORTWAVE TROUGH AMPLIFIES OVER THE MISSISSIPPI
VALLEY. LATE IN THE PERIOD THE TRACK MODEL GUIDANCE IS IN BETTER
AGREEMENT ON THIS SCENARIO...AS THE ECMWF HAS TRENDED EASTWARD
TOWARD THE REST OF THE MODELS THIS CYCLE. THE NEW NHC FORECAST HAS
BEEN ADJUSTED ABOUT A DEGREE SOUTHWARD IN THE FIRST 12 HOURS DUE TO
THE INITIAL POSITION AND MOTION...AND IS THEN BLENDED BACK TOWARD
THE PREVIOUS TRACK BY 48 HOURS. AFTER THAT TIME...THE NHC FORECAST
IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE...AND IS BETWEEN THE
ECMWF ON THE LEFT AND THE GFS AND TVCA CONSENSUS ON THE RIGHT.

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO UNCERTAINTIES
IN THE INITIAL LOCATION AND THE TRACK FORECAST...AND THE FACT THAT
ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED
WITH IT.

FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 16.1N 70.0W 40 KT 45 MPH
12H 24/1800Z 17.0N 71.9W 50 KT 60 MPH
24H 25/0600Z 18.8N 74.1W 45 KT 50 MPH
36H 25/1800Z 20.6N 76.7W 45 KT 50 MPH...INLAND
48H 26/0600Z 22.4N 78.9W 45 KT 50 MPH...OVER WATER
72H 27/0600Z 25.0N 82.5W 55 KT 65 MPH
96H 28/0600Z 28.0N 86.0W 65 KT 75 MPH
120H 29/0600Z 30.5N 87.5W 75 KT 85 MPH...INLAND

$$
FORECASTER BRENNAN

[stormhunter7]

DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT ISAAC REMAINS
POORLY ORGANIZED. WHILE THE 850-MB FLIGHT LEVEL CENTER WAS WELL
SOUTH OF THE PREVIOUSLY ESTIMATED SURFACE CENTER LOCATION...
DROPSONDE DATA SUGGEST THAT THE SURFACE CENTER REMAINS FARTHER
NORTH. FLIGHT LEVEL AND SFMR WINDS SUPPORT MAINTAINING THE
INTENSITY AT 40 KT FOR THIS ADVISORY...WHILE THE AIRCRAFT FOUND A
MINIMUM PRESSURE OF 1000 MB.

[cfltrib]

You have to admit this animation shows "some" error in forecast:
http://images.news8austin.com/media/weather/onair/TRACKER_CARIB-large.gif

[SunnyThoughts]

TwisterFanatic, I was just going to say the same thing. Dropping 8 now...a couple more next advisory...etc until they get it to the correct point. Continuity. Too much of a discrepancy too quickly.

[Kingarabian]

Reasonable disco by the NHC. Dropsonde are always more reliable.

DROPSONDE DATA SUGGEST THAT THE SURFACE CENTER REMAINS FARTHER
NORTH.

[Texashawk]

Wow, is all I have to say. I wish Stewart had been the one in the chair. That was big-time CYA forecasting right there.

[Shuriken]

okay guys, did we misread the recon coordinates or something? They did down it by .8 degrees, but this advisory is still north almost a whole degree.

IMO it's an attempt, and a fairly transparent one at that, to wriggle out from under last night's 16.7 fix with a smooth line, and they'll go with 15.(whatever) at the 8am, and try make a wavy line out of the track instead of a 90-degree left-angle warp-jump kink.

Which means Jamaica, et al, remain outside the cone thinking they're safe for at least another three hours.

[stormhunter7]

well we know where the 850mb center is at...

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 24th day of the month at 08:57Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 10
Observation Number: 07
A. Time of Center Fix: 24th day of the month at 8:39:30Z
B. Center Fix Coordinates: 15°16'N 69°52'W (15.2667N 69.8667W)
B. Center Fix Location: 222 miles (358 km) to the S (180°) from Santo Domingo, Dominican Republic.
C. Minimum Height at Standard Level: 1,417m (4,649ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 45kts (~ 51.8mph)
E. Location of the Estimated Maximum Surface Wind: 21 nautical miles (24 statute miles) to the SE (126°) of center fix
F. Maximum Flight Level Wind Inbound: From 297° at 41kts (From the WNW at ~ 47.2mph)
G. Location of Maximum Flight Level Wind Inbound: 68 nautical miles (78 statute miles) to the WSW (257°) of center fix
H. Minimum Sea Level Pressure: 1000mb (29.53 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 16°C (61°F) at a pressure alt. of 1,523m (4,997ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 1,517m (4,977ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 18°C (64°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 7 nautical miles
Remarks Section:
Maximum Flight Level Wind: 41kts (~ 47.2mph) in the southwest quadrant at 8:05:00Z
Maximum Flight Level Temp: 19°C (66°F) which was observed 18 nautical miles (21 statute miles) to the WNW (282°) from the flight level center

[AJC3]

I'm only gonna say this once. Knock off the jabs at NHC.

[Kingarabian]

Wow, is all I have to say. I wish Stewart had been the one in the chair. That was big-time CYA forecasting right there.

While I love Stewarts disco's. I'm pretty sure the NHC team gets together and discusses what kind of information to put on their published products to the general public -especially with a major threat like this one.

[meriland23]

Something for you all to check out..kinda interesting.. , Aug 24th 5 am, 23rd 8am, 22nd at 2pm ..NHC track

[Shuriken]

well we know where the 850mb center is at...

Product: Air Force Vortex Message (URNT12 KNHC)
A. Time of Center Fix: 24th day of the month at 8:39:30Z
B. Center Fix Coordinates: 15°16'N 69°52'W (15.2667N 69.8667W)
B. Center Fix Location: 222 miles (358 km) to the S (180°) from Santo Domingo, Dominican Republic.
C. Minimum Height at Standard Level: 1,417m (4,649ft) at 850mb

Yep: yesterday's mid-level circ has burrowed down to the 850mb, where the core is now feeding off low-level inflow jets streaming in above any boundary layers.

They found the real storm.

Wow, is all I have to say. I wish Stewart had been the one in the chair. That was big-time CYA forecasting right there.

While I love Stewarts disco's. I'm pretty sure the NHC team gets together and discusses what kind of information to put on their published products to the general public -especially with a major threat like this one.

If the recon 850mb fix runs parallel to the last night's 11pm forecast cone, it goes smack over Jamaica.

[KWT]

Well the models are in good agreement now, but the center that looks like the one to watch is the southern one, recon finding 40-50kts SW winds and the wind field looks amazing compared to last night, much more solid.

Center still wobbling around loads, but it looks like it could be just south of 15N...which clearly changes everything again...

[Stormlover2012]

issac still looks really weak, crazy how carrib is this yr

[wxman76]

If the center really is at 16.1N then it is completely exposed from the convection. I've looked hard on the satellites and I see nothing looking like a LLC. It HAS to be under that convection and I trust the recons. Looks like the 700 center from yesterday is digging in at least to 850 if not the surface. Outflow has greatly increased as has the symmetry. Yeah i think we've got ourselves a storm. I see NHC didn't mention the 60mph 10sec wind speed recon found at the surface. should have gone to at least 50kts IMO.

[LaBreeze]

Well the models are in good agreement now, but the center that looks like the one to watch is the southern one, recon finding 40-50kts SW winds and the wind field looks amazing compared to last night, much more solid.

Center still wobbling around loads, but it looks like it could be just south of 15N...which clearly changes everything again...

Changes everything how?

[meriland23]

Eyyye.. think I need a cigarette...

[meriland23]

if this supposed center goes any further south and west.. ct america may be in play instead of us..

[Shuriken]

[Stormlover2012]

yeah this thing could hit mexico